Composite alloy



Nov. 17, 1953 T. E. LEONTIS ET AL ,13

COMPOSITE ALLOY Filed Aug. 16, 1950 INVENTORSQ Thomas E. Leon/1'5 BY Rober/ S. Busk Patented Nov. 17, 1953 COMPOSITE ALLOY Thomas E. Leontis and Robert S. Busk, Midland,

Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Application August 16, 1950, Serial No. 179,773

4 Claims. (01. 29-1822) The invention relates to a composite metal body of which magnesium is the predominant constituent. It more particularly concerns an improved composite magnesium-base alloy body comprising the binary magnesium-base ma nesium-manganese alloy.

The term magnesium-base-alloy used herein means a magnesium alloy containing at least 80 per cent of magnesium by weight.

One of the most desirable properties of the conventional binary magnesium-base ma nesium-manganese alloy is its lack of sensitivity to stress corrosion. This is evidenced by its ability to sustain a continuous stress at least as high as its yield strength (defined as the stress at which the stress-strain curve deviates 0.2 per cent from the modulus line) over long periods of time while exposed to the outside atmosphere. But the alloy does not possess as high a yield strength as the magnesium-base alloys containing both aluminum and zinc as principal alloying elements. These aluminum and zinccontaining magnesium-base alloys are more widely used for structural purposes than the conventional binary magnesium-base magnesiummanganese alloy, because of their lightness, high yield strength under static loads, and ease of working, in spite of the fact that they are sensitive to stress corrosion and fail, when subjected to a continuous stress while exposed to the outside atmosphere, at stresses which will not cause failure in the conventional binary magnesiumbase magnesium-manganese alloy.

The principal object of the present invention is to provide a magnesium-base alloy product, comprising a binary magnesium-base magnesium-manganese alloy, in which the yield strength is increased to the same order of magnitude as that of the magnesium-base magnesium-aluminum-zinc alloys while retaining the ability to sustain a higher continuous stress for longer periods of atmospheric exposure than that of the magnesium-base magnesium-aluminum zinc alloys.

Other objects and advantages will appear as the description of the invention proceeds.

The invention is based upon the discovery that by die-expressing a comminuted form of the magnesium-base magnesium-manganese alloy in admixture with a comminuted form of the ma nesuim-base magnesium-aluminum-zinc alloy a composite magnesium-base alloy product is obtained which attains the foregoing objectives.

The invention then consists of the improved composite magnesium-base alloy product and method of making the same herein fully described and particularly pointed out in the claims, the following description setting forth several modes of practicing the invention.

in t

In carrying out the invention, the two magnesium-base alloys involved are used in particulate form such as the atomized form. The atomized form may be made by impinging a jet of a cool gas, e. g. natural gas, against a thin falling stream of the molten alloy. Particles coarser than about 10 to 20 mesh sieve size are screened out and preferably also particles finer than about 200 mesh. In the atomized form, the alloys consist of fine round rapidly solidified particles having a very fine grain structure.

The manganese content of the particulated binary magnesium-base alloy may be from about 0.5 to 2.5 per cent, although the preferred proportion is about 1.5 to 1.8 per cent. If desired, calcium, which is sometimes included in alloys of this type, may be present in the usual amounts, e. g. between about 0.05 and 0.5 per cent by weight.

The aluminum content of the particulated magnesium-base magnesium-aluminum-zinc alloy may be from about 1 per cent to about 12 per cent, the preferred proportions being about 3 to 9 per cent. The zinc content of the alloy may be from about 0.5 to 8 per cent, the preferred proportions being about 1 to 3 per cent. As is usual in alloys of this type, manganese may be included, the amount being limited by its solubility in the alloy in accordance with the aluminum content as understood in the art and may be from 0.05 per cent for the higher aluminum proportion up to about 1.4 per cent for the lower aluminum content alloys. About 0.4 per cent of manganese is about the maximum alloyable amount when the aluminum content is about 3 per cent.

The two magnesium-base alloys above described and in particulate form are intimately mixed, as by tumbling the two particulate alloys in a tumbling barrel or in any other convenient manner, prior to extrusion or die-expression. The proportions may vary from about per cent to about 40 per cent of the binary magnesiumbase magnesium-manganese alloy, the balance being the aforesaid magnesium-base magnesiumaluminum-zinc alloy. The preferred proportion is about an equal Weight of each alloy.

The mixture is charged into the heated container of a ram extruder having a suitable size container and die opening to produce a substantial reduction in area. The reduction in area produced, as expressed by the ratio of the cross-sectional area of the container to that of the die opening, has a material efiect on the mechanical properties of the composite extrusion obtained. In general, the higher the ratio the better the mechanical properties. A desirable ratio is at least 30 to 1, although ratios as high as to 1 or more may beused.

The charge on being heated to extrusion temperature is subjected to extrusion" pressure sufiicient to cause the heated metal mixture to be dieexpressed through the die opening. The tem perature of the mixtur of the alloys during ex- 1 trusion is determined mainly by the temperature of the container and may be in the range of temperature usually employed in the conventional extrusion operations with these alloys e. g. from 500 to 1000 F. The preferred temperaturesare about 600 to 700 F.

The rate of die-expression is a; factor in determining the mechanical properties of the ex- 4 The forms of the apparatus shown are conventional. l

By putting a charge of the mixture of particles of the two alloys involved under pressure while at heat, as with the apparatus shown, the

mixture of metal particles is connected but not subjected to further mixing before extrusion. The alloys originally in the charge as individual metal particles become welded together without voids and substantially without mixing. The

particles in the charge do not lose their original distinctive composition except at the surfaces of the union of the different kinds of particles which trusion. In general, the properties of the prodworked in similar manner as by rolling, forging,

pressing, drawing, etc., although the meta-11ographic structure of the composite product is uniquely different from that of theconventional magnesium-base alloy extrusion. Metallographic examination reveals a new type of structure in a magnesium-base alloy article. The structure is essentially multimetallic, each of the individual alloys being in the form of elongated particles all oriented in the direction of the extrusion. The composite alloy extrusions obtained possess an unusual combination of high strength coupled with little or no sensitivity to stress corrosion.

The invention may be further illustrated and explained in connection with the accompanying drawing in which:

Fig. 1 shows a schematic sectional elevation of an extrusion apparatus suitable for use in practi'cing the invention;

Fig. 2 is a similar view to Fig. 1 showing a modification of the apparatus; and

Fig. 3 is a similar view to Fig. 1 showing another modification of the apparatus.

As shown; the apparatus comprises, in its three forms, an extrusion container I adapted to confine a charge. 2 of the mixture'of the particles of the two alloys to be coextruded. The container is provided with a heating element 3. In

' Fig. 1, one end'of the container I is closed by the die plate 4 in which is provided the die opening 5. In this form of the apparatus, the charge 2 is caused to be compacted in the container and extruded through the die opening 5 by application of pressure by means of the dummy block 6 forced into the bore I of the container by the ram 8 to form the composite alloy extrusion 9.

In the form of the apparatus shown in Fig. 2, the container I is closed at one end by the plate ID. The other end of the container receives the die block llhcarried by the hollow ram l2 which forces the die block into the container causing the charge 2 to be compacted and to extrude through die opening I3 to formthe composite alloy extrusion I4 which extends into bore I5 of the hollow ram I2.

In the modification of Fig. 3, the container I is closed at one end by a plate H5. The charge! is extruded as a tubular composite alloy extrusion I1 through the annulus I8 around the die block is while the block is forcedinto the container by the ram 20.

become extended and lengthened during extrusion. At these surfaces during extrusion some intermixing, as by d-ifiusion, takes place between particles of the; two alloys, forming composite alloy, Inthis di l-fusion, some aluminumjrom the aluminum-containing alloy particles difiuses into the binary magnesium-manganese alloy par ticles causing some manganese to be precipitated largely as an'intermetallic compound of alumi- 'num and manganese. I v i The following examples are illustrative of the invention:

EXAMPLE 1 nesium, and the other having a composition of 1:22 per centofmanganese; the balancebeing magnesium, are mixed together in a bailled rotating drum mixer. '-Ihe atomized-particles of the two alloys pass through a ZO'mesh standard sieve and are retained on a 200 mesh standard sieve. The mixture is charged into the 3 inch diametercontainer ot a ram extruder similar to thatof either Fig. 1 or Fig. 2. The container is at 650 Bymeans of the ramysuflicientex- 1trusion pressure is applied to the charge, heated by the container, to 'extrude the charge through thedie opening intoa strip 1 inch by 's inch at the" rateof about five feet of strip per minute.

3 Test .barsarecut from the strip and subjected to tension tests. In one series of the testsfor stress corrosion sensitivity, the bars are put into continuous tension while exposedto a rural at- 50.

mosphere withoutany shielding from sun, wind or rain. In this series of tests, the test bars were located at Greendale, Michigan. The number of days elapsing before the test bars broke, at

. various constantly applied tension loads, calculated to p. s. i., are recorded in Table I.

TABLE I Stress corrosion sensitivity tests of the composite alloyof Example 1 Days outside expo- H H v sureuntil fracture Applied continuous stress in p. s. i.

Test bar 'rbsr bar A B 1 No fractures in 1,095 days and tests still in progress.

TABLE 11! Stress corrosion sensitivity tests of the single magnesium-aluminum-zinc alloy of Example 1 Days outside exposure until fracture Applied continuous stress in p. s. i.

Test bar Test bar Test bar A B O 1 No fractures in 538 days and tests still in progress.

TABLE I11 St ess corrosion sensitivity tests of a single magnesium-manganese alloy Days outside exposure until fracture Applied continuous stress in p. s. i.

Test bar Test bar A B 1 No breaks.

It will be observed from Table I that the composite alloy, and from Table III the binary magnesium-manganese alloy alone, appear to be able to sustain indefinitely a stress at least as high as about 16,000 p. s. i. In contrast, the extrusion formed solely of the atomized magnesium-base alloy of the ternary magnesium-base magnesiumaluminum-zinc type used in the composite extrusion, will sustain indefinitely a stress no greater than about 10,000 or 12,000 p. s. i., as shown in Table II.

In still another series of tests similar test bars of the composite alloy extrusion, and of the extrusions of the individual particulate alloys of the types used in the composite extrusion, were subjected to conventional static tension tests to determine the static tensile yield strength under ordinary conditions. In these tests, a gradually increasing stress is applied until the test bar breaks. The applied stress at which the stress strain curve thus obtained deviates 0.2 per cent from the modulus line, calculated to p. s. i., is the yield strength. The data obtained are set forth in Table IV.

Teen: IV

Extrusion Pep No Composition of extrusion condltmns cent 2 "55 charge elongation l About 1% Mn, balance 580 4 3 23,000

g. 2 3.1% A1, 0.95% Zn, 0.36% 650 150 5 12 29,000

, be cc Mg.

3 Mix of 50 parts of alloy of 560 5 4 35, 000

about 1% Mn, balance Mg; and 50 parts of alloy of 3.1% A1, 0.95% Zn, 0.36% Mn, balance Mg.

T= F.; R=reduction in area; and S=speed of extrusion in feet/mm.

The properties in Table IV show that a higher yield strength extrusion is obtained from the mixture of the two alloys in particulate form than from the particulate form of the individual alloys individually extruded.

EXAMPLE 2 A composite extrusion is made in similar manner to that of Example 1 by extruding a mixture of equal parts of two atomized magnesium-base alloys, one of the two alloys is composed of 6.2% A1, 0.71% Zn, 0.27% Mn, balance Mg; the other is composed of 1.71% Mn, balance Mg. The mixture is extruded at 700 F. at the rate of five feet per minute from a 3 inch diameter container through a die opening 1% inch by inch into composite alloy strip. Under continuous stress in outdoor exposure, test bars cut from the strip indefinitely support loads up to about 18,000 p. s. i. Under similar test condition, an extrusion similarly made of the atomized magnesium-aluminum-zinc alloy alone will support indefinitely a continuous load of only about 12,000 p. s. i. In static tests, the tensile yield strength of the composite alloy extruded at 700 F. is about 29,000 p. s. i. with an elongation of 6 per cent. The tensile yield strength of the atomized magnesium-aluminum-zinc alloy extruded alone at 700 F. is about 25,000 p. s. i., and that of an atomized magnesium-base alloy having a composition of 1.08 per cent manganese, and balance of magnesium, alone is about 23,000 p. s. i. with an elongation of 3 per cent.

EXAMPLE 3 As illustrative of the properties obtainable in composite particulate alloy extrusions within the scope of the invention, the following as-extruded strength data are set forth in Table V. In Table V, alloy A is an atomized magnesium base magnesium-manganese alloy containing about 1.71% Mn, balance Mg (except as indicated in footnote) alloy B is an atomized magnesium-base magnesium-aluminum-zinc alloy containing 3.1% A1, 0.67% Zn, 0.48% Mn, balance Mg. The extrusions are made from a 3 inch diameter container through a round die-forming inchdiameter rod, the apparatus being similar to that of Fig. 1. The properties of the single atomized alloys are shown for comparison.

TABLE V Composition of Extrusion con- Properties of extrusions extrusion charge ditions 1 in 1,000.1). s. 1.

No. Percent 1 ercent Percent A B V T R S v E TYS (1YS TS l 40 60 600 64: 1 12 39 38 47 2 50 50 600 64:1 5 14 38 37 i 46 3 60 40 600 64:1 5 14 37' 37 46 4 70 30 600 64:1" 5 7 35 85 46 5...". 80 20 600 64:1 5 16 34 34 44 Blank" 3 100 600 64:1 5 3 33 33 46 DO 100 600 64:1 5 '15 41 36 47 1 T=cxtrusion temp. F.; R=rcduction in area; S=extrusion speed in feet ,perminute.

TYS=tensilc yield strength; CYS=coInpression yield strength; TS=tensi1c strength; percent E=percent Elongation.

3 Composition: 1.70% Mn, balance Mg.

EXAMPLE 4 This example is further illustrative of the mechanical properties of a composite alloy extrusion within the scope of the invention. An extrusion charge is made of 50 parts by weight of an atomized alloy composed of 5.2% A1, 2.06% Zn, 0.21% Mn, balance Mg, and 50 parts by weight of an atomized alloy composed of 1.7 Mn, balance magnesium. The charge is extruded at 609 1 into inch rod at the rate of 5 feet per minute, the ratio of the reduction in area being 64 to 1. Both the tensile yield strength and the compression yield strength of the composite alloy extrusion obtained is 37,000 p. s. i. The extrusion made under the same conditions of the atomized magnesium-aluminumezinc alloy alone has ten.- sile yield strength of 34,000 p. s. i. and a compression yield strength of 32,000 .p. s. i. The extrusion made under the same conditions of the atomized magnesium-manganese alloy has a tensile yield strength and compression yield strength .01 33.000

EXAMPLE 5 The-following tabulation (Table VI) sets forth a number of composite extrusions formed by extruding mixturesof 50 parts of an atomized magnesiurn-ibase magnesium-manganese alloy, and 50 parts of a magnesium-base alloy composed of magnesium alloyed with aluminum zinc, and manganese, this alloy having the composition shown in the table.

In the mixtures numbered 1 to 5, inclusive, of Table VI, the manganese content of the magnesium-manganese alloy was 1.7%, in mixture Number 6, the 'manganese content of the magnesium-manganese alloy was 1.6%. The properties of the resulting composite extrusion of inch rod made at 600 F. at 5 feet per minute by extruding the compositions with a 64 to 1 reduction in area are shown in the Table VI.

I a o endingapplicat on er a no. 179.7 2.

filed August 16, 1950. we have described and claimed a composite high strength metal article iormed y diexpr ng a mi tu e of an atomized binary magnesium-base magnesium-manganese alloy and a .comrninuted magnesium-sow,- ble metal including aluminum either in elemental form or alloyed with magnesium. In the present invention, aluminum is used in alloyed form, the.

alloy being a magnesium-base alloy in which the aluminum is alloyed both with magnesium and zinc, and manganese may be included, if desired.

Among the advantages of the invention are that it makes possible the production of a metal body having the characteristic lightness and strength of the conventional magnesium-base magnesiumr-aluminumi-zinc alloys with the low stress corrosion sensitivity characteristic of the conventional binary magnesium-base magnesiummanganese 'alloy as well as generally greater strength than the conventional magnesium-base binary magnesium-manganese alloy.

We claim:

1. The method of making a solid composite article comprising magnesium alloyed with man ganese which comprises forming a mixture of a particulated magnesium-base binary magnesiummanganese alloy containing from about 0.5 to 2.2 per cent of manganese and up to 0.5 per cent of calcium, the balance being magnesium; and a particulated magnesium-base magnesium-aluminum-zinc alloy containing from 2 to 10 per cent of aluminum, 0.5 to 4 per cent of zinc, and up to about 1.4 per cent of manganese, the balance being magnesium; said mixture containing about 40 to parts of the said binary magnesiummanganese alloy per parts of the said mixture; and die-expressing the mixture in solid condition at a temperature of at least 500 F.

2. The method according to claim 1 in which the binary magnesium-manganese alloy contains 1.5 to 1. 8 per cent of manganese and the magnesiumbase magnesium-aluminum-zinc alloy contains 3 to 9 per cent of aluminum, 1 to 3 per cent of zinc, and up to 0.4 per cent of manganese.

3. The method according to claim 1 in which the said mixture contains about 50 parts of the said binary magnesium-manganese alloy per 100 parts of the said mixture.

4. A composite metal body consisting of at least two particulate alloys one of the two alloys being a binary n1agnesiun1-base magnesium-"nanganese alloy containing from about 0.5 to 2.2 per cent of manganese and up to 0.5 per cent of calcium, the balance being magnesium, the other being a magnesium-base magnesium-alu1ninumzinc alloy containing from 2 to 10 per cent of aluminum, 0.5 to 4 :per cent of zinc, and up to about 1.4 percent of manganese, the balance being magnesium, the two particulate alloys being in the proportion of about 40 to 90 parts of the said binary alloy per 100 parts of the composite metal body and the particles of each of the said two alloys being elongated, orientated in the same direction, and welded into an integral solid.

THOMAS E. LEONTIS. ROBERT S. RUSK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,02 ,767 Jefiries et a1 Dec. 17, 1935 2,287,251 Jones June 23, 1942 OTHER REFERENCES Treatise .on Powder Metalli' rgy, by .Goetzel, vol. 2, pages 500, 740, 741, 1950. 

4. A COMPOSITE METAL BODY CONSISTING OF AT LEAST TWO PARTICULATE ALLOYS ONE OF THE TWO ALLOYS BEING A BINARY MAGNESIUM-BASE MAGNESIUM-MANGANESE ALLOY CONTAINING FROM ABOUT 0.5 TO 2.2 PER CENT OF MANGANESE AND UP TO 0.5 PER CENT OF CALCIUM, THE BALANCE BEING MAGNESIUM, THE OTHER BEING A MAGNESIUM-BASE MAGNESIUM-ALUMINUMZINC ALLOY CONTAINING FROM 2 TO 10 PER CENT OF ALUMINUM, 0.5 TO 4 PER CENT OF ZINC, AND UP TO ABOUT 1.4 PER CENT OF MANGANESE, THE BALANCE BEING MAGNESIUM, THE TWO PARTICULATE ALLOYS BEING IN THE PROPORTION OF ABOUT 40 TO 90 PARTS OF THE SAID BINARY ALLOY PER 100 PARTS OF THE COMPOSITE METAL BODY AND THE PARTICLES OF EACH OF THE SAID TWO ALLOYS BEING ELONGATED, ORIENTATED IN THE SAME DIRECTION, AND WELDED INTO AN INTEGRAL SOLID. 